Offset lithographic printing is a widely used printing method. This is in large part due to the relative ease, with which offset lithographic printing plates can be produced. Contemporary offset lithographic plate preparation includes using specially prepared masking films, to selectively harden or soften (according to the chemistry of the plate) portions of the surface of the plate using imaging by exposure to ultra-violet radiation. The plate is subsequently developed during which the soluble regions of the plate surface are washed away.
With the onset of digital technology, computer generated digital information is printed onto plates directly, but the plates still employ the masking films. Contemporary masking films are silver based, and as such exhibit substantial drawbacks.
Initially, these films are expensive, as silver is a non-renewable resource, and are extremely vulnerable to price fluctuations based on market conditions. The chemicals for processing silver films are also expensive. An even greater problem is that the spent silver and chemical wastes from processing are highly toxic and thus, environmentally harmful. Proper disposal of these materials is expensive, for it must be done in an environmentally safe manner, by sophisticated methods. Additionally, silver films are temperature and visible light sensitive, and thus, processing must always be performed and the films maintained under controlled conditions.
Another approach involves laser imaging of printing blanks. For example, U.S. Pat. No. 4,054,094 (Caddell, et al.) discloses a system for imaging a printing member (or blank), the blank having a thin hard hydrophilic coating on a polymer, this polymer being coated on a polymeric or metal base. A high energy, carbon-dioxide laser etches (or ablates) away the layers to expose the material of the base, this material being oleophilic.
In U.S. Pat. No. 4,693,958 (Schwartz, et al.), high energy laser radiation of 10 watts, hardens a printing member (plate) having a water soluble coating. The nonimaged and unhardened non imaged areas are washed away to expose a hydrophilic aluminum substrate. The film thickness to be hardened is at least 0.2 microns (micrometers).
A further trend in offset printing technology is market based, and in particular toward short run printing. This is because the number of copies printed at a single location is declining, due to the high cost of warehousing and shipping. Rather, local printing in short runs is becoming popular, as it saves on warehousing and shipping, and in particular postage.